Days before an advisory panel to the Food and Drug Administration is expected to meet to discuss the Merck COVID-19 pill, the company revised the results of a previous study to reflect the pill is less effective than previously thought. The original Merck study, which was released early last month, found Molnupiravir reduced hospitalizations and deaths by half in people recently infected with the coronavirus. The revised results, which include over 1,400 patients instead of just 775, bumps the effectiveness down to 30%.

Despite this, “the adverse event profile for Molnupiravir remained consistent with the profile reported at the planned interim analysis,” according to a news release from Merck. “The interim analysis and the additional analyses support the efficacy and overall favorable benefit-risk assessment of Molnupiravir for the treatment of mild to moderate COVID-19 in adults at high risk for disease progression.”

While the FDA has acknowledged the Merck COVID-19 pill is at least partially effective against the virus, the administration wants its advisory panel to weigh that effectiveness against any potential safety risks. Those risks include possible toxicity, birth defects and other potential problems during pregnancy. Based on those potential risks, identified in an FDA review, the FDA will ask its advisers if the Merck COVID-19 pill should only be offered during certain pregnancies, or not during pregnancy at all.

The FDA also asked the committee to weigh in on concerns over whether the pill could encourage the virus to mutate, as well as how those concerns could be mitigated. Regulators also noted that Merck collected far less safety data overall on its pill than was gathered for other COVID-19 therapies.

Next Tuesday’s meeting will mark the first time regulators have publicly reviewed a COVID-19 pill. Pfizer is right behind Merck in getting a COVID-19 pill approved. Earlier this month, Pfizer announced it is asking the Food and Drug Administration for emergency use authorization for the company’s pill. The request came after results of a Pfizer study found the pill “caused an 89% reduction in risk of COVID-19-related hospitalization or death”.